This paper discusses the acquisition of knowledge by one generation from another, and the problems inherent in the process. The difficulties are seen as falling into three areas: (i) the difficulty of understanding the knowledge itself; (ii) the difficulty that a fact or a theory becomes an internal object subject to all the vicissitudes of object relations; and (iii) the difficulty of finding a training method that will enable the learner to assimilate knowledge and use it judiciously rather than to swallow it in an uncomprehending way. Examples are drawn from the history of ideas in general, and from the author's experience of therapeutic communities, particularly the Cassel Hospital. The danger of allowing a body of knowledge to become, in its passage from one person to another, a mere set of never-to-be-questioned beliefs is illustrated. The common frailties of both trainers and trainees are discussed and methods suggested for understanding and overcoming them.